Embodiments of the present invention pertain to resistive heaters, apparatus incorporating resistive heaters and methods of heating substrates such as semiconductor wafers.
Resistive heaters are widely employed in the heating systems of chemical vapor deposition (CVD) systems. Temperature uniformity is an important consideration in CVD processes, and as a result, multi-zone resistive heaters have been developed to provide greater control over the heating characteristics of the heating apparatus in CVD systems. For example, U.S. Pat. No. 6,646,235 to Chen et al., the entire content of which is incorporated herein by reference, discloses a CVD resistive heater that has an inner zone and an outer zone, where the outer zone completely surrounds the inner zone. By providing these concentric zones, it is possible to compensate for the different rates of heat loss exhibited by the inner and outer regions of the heating apparatus, and so provide more uniform heating across the entire diameter of a wafer.
Even slight variations in temperature uniformity across a wafer, on the order of just a few degrees Celsius, can adversely affect a CVD process. Limitations in manufacturing tolerances make it extremely difficult to make a multi-zone heater that has consistent heating power characteristics around its entire circumference. Hence, at a given radius, one region of the resistive heater may provide more or less heating power than another region at that same radius. The resulting temperature variations introduce one layer of complexity that must be controlled to insure process repeatability across multiple wafers for the same resistive heater. Moreover, putatively identical resistive heaters display different heating power characteristics amongst themselves, which introduces yet another layer of complexity that is adverse to process repeatability. In addition, the CVD chamber itself may have regions that exhibit irregularities in temperature uniformity, introducing further possible temperature irregularities.
Accordingly, it would be desirable to provide a resistive heater that can provide compensation for heating irregularities to enhance process repeatability in high temperature deposition systems, such as reactors incorporating CVD chambers.